White light tube



April 11, 1933. E K 1,903,494

WHITE LIGHT TUBE Filed Dec. 12, 1929 FIGJ.

FIG.2.

LEO L. BEG/f Patented Apr. 11, 1933 UNITED STATES PATENT OFFICE LEO L. BECK, OF WESTIIELD, NEW JENSEY, ASSIGNOR, BY MESNE ASSIGNMENTS, TO GENERAL TUBE LIGHTS CORPORATION, OF NEW YORK, N. Y A CORPORATION 01' nmawm wm'ra LIGHT TUBE Application fled December 18, 1829. SerialNo. 413,471.

This invention relates to positive column tubes which emit a light which does not distort the natural colors. It is a well known fact that any illumination regardless of its source which is lacking in certain of the color rays cannot bring out those colors, the rays of which are lacking in the light. Such co ors are distorted in that they may appear to be black or they may even appear to be a totally different color from the color which they normally possessed in a light having all the color rays of a normal spectrum. This failure to give certain colors of the spectrum any color or their true color or even their true shade of color in that the colors may be a lighter or a darker shade than the properly would have in a normal light, pro uces what will be termed herein as distortion. A light which does not distort the natural colors has been described in my copending application Serial No. 373,916 filed on June 26, 1929, and this invention is a continuation in part of the disclosure in that application.

It is an object of this invention to produce a positive column tube containing hellum and neon which emits a light which does not distort the natural colors and which contains as a part of the gaseous content of the tube a gas having a low voltage gradient.

Another object of the invention is to produce a positive column tube which emits a light which does not distort the natural colors of the spectrum which tube contains a gas having a low voltage gradient which does not in turn distort "the natural colors and having an electrode which cooperates with the gaseous contents of the tube to produce a tube operative at low voltages without affecting the light emitted by the gases in the tube.

The invention will be more apparent from the following description taken in connection with the drawing in which:

Figure 1 shows a positive column tube provided with a low voltage electrode.

Figure 2 shows a positive column tube having a hot cathode type of electrode. 7

The positive column tube of which this invention pertains consists of a transparent envelope 1 having electrodes within the enve'lope at either end. These electrodes may be of metal such as copper, iron and nickel, and may bepositioned at either end of the envelope, one such electrode 2 being shown at one end of the positive column tube illuskali type may be used at one end and the tube illuminated by a direct current. The preferred type of alkali low voltage electrode would consist of an alkali metal pool 3 such as lithium, sodium, potassium or caesium or a mixture of two or more of these metals. An electrode 4 may be immersed within the alkali metal to more efliciently transfer the electric current from the conducting wire 5 which is carried through the glass seal of the envelope to the alkali metal pool. The tube containing the alkali pool electrode is preferably enlarged and such enlar ed ortion 6 comprises the container for t e a kali metal pool. The electrodes 2 and 3 are connected to a source 7 of electrical energy and an adjustable resistance 8 may be provided to adjust the current passing through the tube.

The alkali metal electrode described above has a tendency to cause some discoloration of the light of the tube so that some distortion of the natural colors of the spectrum results. The hot cathode type of electrode however does not so aflfect the light emitted by the tube so that from this standpoint the hot cathode electrode is somewhat more suitable.

Such a cathodeis shown in Figure 2 in which the tube. The supports 16 for the heating element 15 are connected to a source of electrical energy such as the transformer 19. The electrical circuit may be arran ed so that the filament 15 may be automatically heated by the discharge current or by an independent source of electrical current, at the will of the operator. If the filament is to be heated by such independent electrical source switches 28 and 20 are closed and the electric current then flows through the transformer 19 20 the connection indicated by the dotted line 22. Switches 20 and 26 may then be opened and connection established between the wires 36 and 34 by means of the connection indicated by the dotted line 24. Under these conditions discharge current is permitted to pass through the electrode 13, through the wires 32 and 16, through the heating filament .15, through the wires36, 24 and 34, through the resistance 18, source of current 17 and then through the anode, not shown, and through the positive column. Where it is desired to have the heating filament automatically heated by the discharge current it is desirable to employ the independent source of heating current of which the transformer 19 constitutes a part, in order to assist in starting the tube and in this case when the tube strikes or is lighted the independent source of heating current may be discontinued and the filament heated solely by the discharge current by changing the connection as described. On the other hand if the filament is to be heated during the operation of the tube by the independent source of heating current connections are so made as described so that current from the independent source of heating current will continue to flow from the heating filament 15 and thereby heat the cathode 13.

In order to secure a light from a positive column tube which does not distort the natural colors of objects viewed in the light emitted by the tube, it is necessary that the tube contain gases which when illuminated produce a light which contains all the colors of the spectrum and therefore properly brings out all the colors of the normal daylight spec- I trum viewed in this light in their true color and in their true shade without distortion or at most without material distortion.

The rare gas neon when illuminated in a positive column tube in its pure state emits a characteristic orange red color. This gas therefore contains red and orange rays but is lacking in yellow and blue rays. Consequently, a normal spectrum viewed under a osltive column tube charged with more or ess pure neon so that the neon emits its characteristic color, illuminates the red and .red.

By mixing these two gases and obtaining a mixture within a positive column tube in which the emitted light contains the proper portion of red, orange, yellow, green, blue and violet rays, a light is produced which does not distort or materially distort the natural colors of the spectrum. It has been found that by operating at relatively high current densities, the potential fall through the positive column is thereby reduced and according to the present invention the current density is adjusted to a suitable range of value, as from 0.03 ampere to 1.25 amperes per square centimeter of tube cross section of the positive column. It is however highly desirable to correlate the per cent of neon in the as mixture with the articular current density employed inasmuc as with increased current densities there is a tendency toward a disturbance of the balance between the proportion of current carried by the helium and neon respectively at lower current densities with a consequent disturbance in the character of the spectrum of the mixed gases of such a nature that the intensity of the neon light decreases and that of the helium increases. To offset this change and toy maintain the desired spectrum composition of the light emitted by the mixed gas, the proportion of the neon is in-' creased as the current density is increased so that corresponding to the range of current densities specified above, the range of percentage of neon may vary as for example from 2 to 8%. For exam le a typical gaseous mixture adapted to y1eld white light at light which does not distort natural colors and which is operative at lower voltages and higher efiiciency, a gas having a low voltage a current density in the neighborhood of 0.40 p

gradient ma be mixed with the gases helium and neon. uch low voltage gases which are suitable for this purpose include the gases argon, krypton and xenon. These low voltage gases must be in such proportion, however, that they, in turn, do not emit a light which masks the characteristic neon and helium color but blends to produce a light which does not distort the natural colors. The addition-of argon to the helium and neon of such a tube in a proportion not to exceed one-half of one per cent of the gaseous tube contents lowers the voltage gradient of the gaseous contents of the tube and renders it more eflicient and yet the argon does not emit suflicient rays of its characteristic color to destroy the balance of the helium and neon to emit a light which does not distort the natural colors.

The gases krypton and xenon similarly reduce the volta e adient of the gaseous contents of the tu i l 1t these two gases have an even lower voltage gradient than ar on. As a result of this lower voltage gra ient of krypton and xenon there is a tendency on the part of these gases if used in as large proportion as argon to contribute their characteristic color to the color rays of helium and neon so that'some distortion of the natural colors of the spectrum results. In order to roduce .a positive column tube which emlts a light which does not distort the natural colors and in which the low voltage gases krypton or xenon are used, the percentage of krypton for best results should not exceed about 0.30 per cent of the gaseous contents of the tube and that of xenon about 0.15 per cent. With these proportions of xenon or krypton the light emitted by the positive column tube is substantially unaffected and the colors illuminated this light appear undistorted or substantia 1y undistorted.

Having described my invention it is to be understood that the invention is not to be limited by'the preferred disclosure or any specific applications of the invention set forth herein excepting as limited by the ac- 1.'A positive column tube for emitting a.

light which does not distort the natural colors comprising a transparent envelope, electrodes within the envelope, anda mixture of helium, neon, and a gas selected from the grou consisting of krypton and xenon within t e envelope, said helium comprising from about 92.00 to 98.00 per cent of the gaseous contents of the tube.

2. A positive column tube for emitting a light which does not distort the natural colors comprising a transparent envelope, electrodes within the envelope, and a mixture of the gases helium, neon, and krypton within the envelope, said helium comprising from about gas comprising not more than about 0.30 per cent of the gaseous contents of the tube.

4. A positive column tube for emitting a light which does not distort the natural colors comprising a transparent envelope, electrodes within the envelope, and a mixture of the gases helium, neon, and krypton within the envelope, said helium comprising from about 92.00 to 98.00 per cent an the krypton comprising about 0.30 per cent of the gaseous contents of. the tube.

5. A positive column tube for light which does not distort the natural colors comprising a transparent envelope, electrodes within the envelope at least one of which is a low voltage electrode, and a mixture of helium, neon and a gas selected from the oup consisting of krypton and xenon withm the envelope, said helium comprising from about 92.00 to 98.00 per cent and the sai selected gas comprising not more than about per cent of the gaseous contents of the 6. A ositive column tube for emitting a light which does not distort the natural colors comprising a transparent envelope, electrodes within the envelope at least one of which is a low voltage electrode, helium, neon and krypton within the envelope, said helium comprisin from about 92.00 to 98.00 per cent and the rypton comprising about 0.30 per cent of the gaseous contents of the tube.

7. A positive column tube for emitting a light which does not distort the natural colors comprising a transparent envelope, electrodes within the envelope, and a mixture of helium, neon and xenon within the envelope, said helium comprising from about 92.00 to'98.00 per cent an the xenon comprising not more than about 0.15 per cent of the gaseous contents of the tube.

8. A sitive column tube for emitting a light which does not distort the natural colors comprising a transparent envelope, electrodes within the envelope at least one of which is a low voltage electrode, and a mixture of helium, neon and xenon within the envelope, said helium comprising from about 92.00 to 98.00 per cent and the xenon comprising not more than about 0.15 per cent of the gaseous contents of the tube.

In testimony whereof I aflix my signature.

LEO L. BECK.

emitting a and a mixture of 

